CLOUDP-451851: Remove omitempty from planned flag

[danielblanco96]

Ticket

CLOUDP-451851

Description

The planned flag was never sent false because of the omitempty in the struct. This PR removes it.

Testing

Before:

➜  mongodb-cli git:(main) ./bin/mongocli ops-manager standby-clusters failover
? Are you sure you want to trigger a failover of the standby cluster at s3://test-mcli/dr_status_prodRS.json? The standby cluster will be promoted to active. Yes
Failover triggered for standby cluster 'prodRS'. State: PromoteStandby.
➜  mongodb-cli git:(main) ./bin/mongocli ops-manager standby-clusters describe -o json
{
  "state": "PromoteStandby",
  "previousState": "Standby",
  "clusterName": "prodRS",
  "version": "2",
  "lastModified": "2026-09-29T06:46:12Z",
  "schemaVersion": "1"
}

After:

➜  mongodb-cli git:(CLOUDP-451851_remove_omitempty_planned_flag) ✗ ./bin/mongocli ops-manager standby-clusters failover
? Are you sure you want to trigger a failover of the standby cluster at s3://test-mcli/dr_status_prodRS.json? The standby cluster will be promoted to active. Yes
Failover triggered for standby cluster 'prodRS'. State: PromoteStandby.
➜  mongodb-cli git:(CLOUDP-451851_remove_omitempty_planned_flag) ✗ ./bin/mongocli ops-manager standby-clusters describe -o json
{
  "state": "PromoteStandby",
  "previousState": "Standby",
  "clusterName": "prodRS",
  "version": "2",
  "lastModified": "2026-09-29T06:52:24Z",
  "schemaVersion": "1",
  "planned": false
}

Tested both the missing planned flag and the planned=true cases